A prior genomic linkage scan in Pima Indians indicated an obesity susceptibility locus on chromosome 11q23-24 (LOD=3.6). There was also evidence that the same genomic region contained a susceptibility locus for type 2 diabetes mellitus (T2DM)(LOD=1.7). Bivariate linkage analysis for the combined phenotype diabesity gave the strongest evidence for a disease locus (LOD= 5.2). The region of linkage spans 24 Mb. To narrow this region, single nucleotide polymorphisms (SNPs) were genotyped in 1300 subjects at a 5 kb density, across the entire 24 Mb, for linkage disequilibrium (LD) mapping. Several of our most interesting SNPs were genotyped in the FUSION study of Finns, independent case/control samples for either T2DM or obesity from Botnia, Helsinki, and Malmo, a large collection of metabolically phenotyped Caucasians from Denmark, Caucasian children from the Leipziger School Children study, Caucasians from the UK (Oxford), Mexican Americans from the VAGES study, and Mexican Americans from Starr County. Results from these replication groups for genes in our region of linkage on chromosome 11q23-25 have shown that variants near ETS-1 on chromosome 11 have replicated in three out of five studies. A variant in TREH on chromosome 11 showed significant associations in 6 out of seven studies, but the risk allele was inconsistent among the various ethnic groups, so it remains debatable whether this variant replicated. [unreadable] My lab has further followed up on significant associations identified by LD mapping by directly sequencing 74 positional candidate genes under the peak of linkage on chromosome 11q23-25. Variation within IGSF4 and ETS-1 were the most strongly associated with BMI and variation within TREH was the most strongly associated with T2DM. We have completed functional analysis of variants within TREH, which encodes trehalase. We measured serum trehalase activity in 570 non-diabetic subjects and found that trehalase activity was highly associated with a non-synonymous Arg486Trp variant and a promoter variant at -100 b.p. (p=10-12 and p=10-15, respectively, adjusted for age, sex, heritage and family membership). Haplotype analysis showed that subjects who were homozygous for 3 variants (Trp486, Ala389, and C at -100 b.p.) had the lowest trehalase activity and had the lowest prevalence of T2DM. However, in a prospective study, we were unable to demonstrate that a low plasma trehalase activity (independent of genotype) predicted the development of T2DM. Therefore, we believe we have uncovered the genetic basis for the bimodal appearance of trehalase activity (14), and although these variants are associated with T2DM, they may not be causative for T2DM.[unreadable] We have also performed funtional studies for variants in a highly conserved, intergenic region distal to ETS-1. These variants are associated with BMI in Pima Indians, where the association becomes significantly greater among the families with evidence for linkage on chrom. 11q23. My lab has been doing in vitro functional studies and have shown that this region contains enhancer activity, and I have collaborated with the Mouse Metabolism lab of NIDDK that has shown that female ETS-1 hemizygous mice have significantly higher body fat as compared to their wild type littermates.[unreadable] We have recently genotyped variation within TREH, IGSF4 and ETS-1 in an independent, population-based group of Pima Indians, and found that the assocation of TREH with T2DM and IGSF4 with BMI strongly replicated.